Anomal breite Regenbögen (keine Bilder)

[Elmar Schmidt]

Hallo,

auf einer Autofahrt von München nach Hause durchquerte ich Schauer um Schauer. Gegen 16:00 auf der A81 bei Ludwigsburg fiel mir am Horizont ein diffuser und breiter (ca. 4-5 Grad) linker Regenbogenteil auf. Es war der Sekundärbogen. Kurz danach erschien auch der Primärbogen in meinem Blick, und der war in etwa genauso breit und diffus und gar nicht mal so viel heller. Bei beiden war aber die übliche Farbfolge gut erkennbar.

Leider war ich allein, und es gab auch keine Gelegenheit zum Anhalten und Fotografieren

Der Punkt ist der: die Sonne hinter mir war zu dem Zeitpunkt durch Wolken in ein gleißendes Leuchtfeld vergrößert worden, was natürlich die Verbreiterung der Bögen zwanglos erklärt. Daß mir so etwas noch nie aufgefallen ist, heißt sicher nicht, daß das ungewöhnlich ist. Und das wäre meine Frage in die Runde, ob es nämlich schon ähnliche Sichtungen hierzu gab.

Gruß, Elmar


PS: mir fiel dann aber noch was ein. Es gibt ja auch immer wieder mal Situationen, wo sich die durch hohe Wolken in ein Leuchtfeld wie oben geschildert verbreiterte Sonne durch Löcher in niedrigen Wolken in mehrere diskrete Lichtquellen "zerlegt", welche durchaus einige Grad Abstand haben könnten. Damit wären doch unter Umständen einige der im Spaltbogenumfeld vorgestellten Mehrfachbögen erklärbar, wobei die häufig gegebene Konzentrizität aber an den Zufall geknüpft sein müßte, daß die Wolkenlöcher vertikal angeordnet sein müßten. Alex[ander Haußmann] verfügt ja wohl über die beste Bildersammlung anomaler Regenbögen und könnte die vielleicht mal daraufhin abklopfen.

[Timo Kuhmonen]

fyi.

I have not seen that kind of rainbow anomaly myself, although there could be ones...

I have made search in Taivaanvahti for all observations classified as rainbow anomaly ("anomaalinen sateenkaari" in finnish). The search time begins at 1.1.1990. Totally 37 observations were found.
https://www.taivaanvahti.fi/observation ... /desc/0/20

PS:
in some of the rainbow anomaly observations, M. Riikonen has mentioned a name William R. Corliss. Could be interesting to read some of his book(s), like this one.
https://en.wikipedia.org/wiki/William_R._Corliss
https://www.amazon.com/Mirages-Anomalou ... 0915554127

[Elmar Schmidt]

Thanks Timo,

for diving through my German language text, and for the link to this collection. Mostly, it contains classic split bows, where it now seems undisputable, that oblate drops are the effect's cause, as the second order is always unaffected, quite like predicted in simulations from Alex and others.

My observation showed a strange broadening of both orders, however, which IMHO stemmed from the sun being smeared out to a wider smudge of bright light by high clouds. I would doubt, that this has never been seen or was never photographed before.

For more bizarre effects, we are aware of Corliss' collection, too, although it consists of drawings for most. Some of these sightings are clearly reflected or reflection bows. Others, like multiringed bows might be either split bows or caused by multiple light sources or both. (Or halos, or fakes, or pranks...) That was the point of my PS.

Kind regards, Elmar

[Alexander Haußmann]

Hi Elmar and Timo,

the Corliss book (the one dealing with atmospheric optics) is right here on my shelf. Some of the stuff is really strange, like the "odour of the rainbow" or "sandbows" in the desert. Other reports in it are not that enigmatic anymore from today's viewpoint.

Concerning Elmar's observation: The cloud acting as a secondary light source is certainly an interesting idea. There would not only be the broadening due to the angular size but also the full complexity of "Minnaert's apple-shaped cigar" describing rainbows in divergent light. It would certainly require some careful arrangement of the bright cloud, the observer and the raindrops to create a rainbow near the familiar location in the sky.

Last Friday I saw a superposition of an ordinary rainbow in a somewhat distant shower and one in the spray from the wheels of nearby cars while driving on the "Autobahn". The spray bow was much broader with a white streak in it (as expected from smaller drops) and extended below the horizon, but was due to direct sunlight as well. Needless to say, there was no opportunity to take photos.

Also thanks to Timo for providing the collection of pictures from Suomi. I would not have been able to formulate the correct keywords for the search. But as Elmar already noted, these are mostly "classic" split bows. The stranger stuff seems to be restricted to warmer climates (southern China, Japan, Florida...).

Best regards,
Alex

[Timo Kuhmonen]

In URSA halomeeting at 2006 (Artjärvi, Finland), there was one presentation held by Yuji Ayatsuka.
https://www.ursa.fi/ilmakeha/tapaamiset ... -2006.html

There is three cases of rainbow anomaly with explaining text...
http://www.asahi-net.or.jp/~cg1y-aytk/a ... omaly.html

It is on japanese language. Google does not make a complete translation of the web page, smaller text sections do make translation. The distorted bow(s) looks interesting. Yuji did show these images on presentation at meeting.

PS.
Is there any known documentation, of the thunderstorm and/or nearby lightning affecting to rainbow(s)? I mean case where is area of good reflection drops would be near lightning channel. Sudden temperature rise there in lightning strike would would create pressure wave, in form of sound. Is it noticed ever, that this pressure wave would distort rainbow droplets temporarily ? If yes, how this would be seen on a bow...?

[Alexander Haußmann]

Hi Timo and Elmar,

I remember that the pictures by Yuji Ayatsuka were also shown in our Meteoros journal, together with a translation into German. I think that these observations are really difficult to explain. From my current understanding they would require drop distortions, oscillations and/or tilts that vary spatially throughout the shower. This would introduce so many free variables that in the simulations any output could be generated.

Concerning Elmar's hypothesis: If we disregard any divergent light effects for the moment, then a "typical" rainbow from a light source with an angular diameter of 2° would look as such:

This is the reference case, with an angular diameter of 0.54°:

But as mentioned, if a cloud in about 3 km distance acts as the light source, and the rain shower would be at a distance of 0.5 km from the observer, then wen need to think about "Minnaert's apple".

Best regards,
Alex

[Elmar Schmidt]

Hi Alex and Timo,

it is a real pity, that I must now only remember my sighting. However, it is still clear, that both primary and secondary rainbows (actually, as the sun was still high in the sky, just their quite slanted "feet" in a radius of maybe 15-20 degrees) appeared equally broad and diffuse, like in the simulated first picture shown above

Regarding Minnaert's apple or cigar, I want to add, that its prerequisite might not have been met here, because a bright aureole around the sun emits mostly forward scattered light instead of illuminating half the solid angle isotropically. This is similar to the case of a night rainbow produced by weakly divergent car headlights as discussed here by AKM's Christian Fenn:

https://old.meteoros.de/rainbow/rbdiv_1.htm

A full Minnaert's apple case, even producing reverse rainbows, was observed by our Christoph Gerber and explained here again by Christian:

https://old.meteoros.de/rainbow/rbdiv_2.htm

In concluding, it may suffice to invite others to look for and photograph rainbows under equally diffuse lighting conditions.

Kind regards

Elmar